High sound absorption of porous aluminum fabricated by spacer method

Porous aluminum with a density of 0.27g∕cm3 was produced by the spacer method. The sound absorbency of the material is significantly improved by inserting an air gap between the sample and the rigid back surface; in this manner, a sound absorption coefficient near unity can be achieved over a significant portion of the audible range. The present data agree with the theoretical analysis in the previous study by Lu et al. [J. Acoust. Soc. Am. 108, 1697 (2000)]; this in turn shows that the present results can largely be attributed to the size (= approximately 50μm) of apertures connecting pores in the material.